Grinding machine



Feb. 17, 1959 o. BRETSCHER GRINDING MACHINE 2 Sheets-Sheet 2 Filed Aug. 9, 1954 INVENTOK. arm fizz-730% BY%% Fig.4

United States PatentO GRINDING MACHINE Otto Bretscher, Geriafingen, Switzerland, assignor to Gesellschaft der Ludw. on l'loilsclren Eisenwerke A. 6., Gerlahngen, Switzerland, a Swiss company Application August 9, 1954, Serial No. 448,461

Claims priority, application Switzerland August 10, 1953 16 Claims. (Cl. 51-465) The present invention relates to means for feeding in the grinding wheel of grinding attachments using cup grinding wheels.

In known attachments of this type the grinding wheel spindle is mounted in a rest guided in slide bars, which rest is moved along a direct path towards the workpiece by means of a threaded spindle and nut. This results in tensions being produced during the advance of the said rest so that the advance is effected jerkily and thus generally overshoots the desired dimension which should only be, for instance, 0002-0003 mm. at the end of the grinding.

it is, therefore, one of the principal objects of the present invention to provide means avoiding the aforesaid disadvantages and drawbacks and facilitating highly accurate control of the extent of travel of a grinding wheel toward a work piece to be subjected to grinding operations.

it is another object of the present invention to provide means contributing to a greatly simplified and highly eiiicient control arrangement for regulating thefeed of a grinding wheel toward a work piece, said arrangement includinggauging means having an actuating element movable together and coextensively with said grinding wheel, whereby the length of the path of travel of said grinding wheel can be accurately predetermined.

Still another object of the present invention is to provide means enabling the grinding allowance for each work piece to be determined within extremely narrow tolerance limits by first gauging means, and further enabling the grinding action or" the grinding wheel to be determined to the same degree of accuracy by second gauging means independent of but coordinated to said first gauging means.

. A further object of the present invention is to provide means contributing to a novel and compact attachment for use with grinding machines in combination with the aforesaid first and second gauging means, electrically perated signal means being provided to facilitate control of the machine inresponse to predetermined actuation of-said second gauging means.

These and other objects of the invention will become further apparent from the following detailed description, reference being made to the accompanying drawing, showing a preferred embodiment of the invention.

In the drawing:

Fig. 1 is a crosssectional view taken through the attachment.

Fig. 2 is a sectional View taken along line I-I in Fig. 1.

Fig. 3 is a detail of the structure for adjusting the shaft. i

Fig. 4 is an electrical wiring diagram of the device of the invention. t

Referring now to the drawing in greater detail, a slide 2 is shiftably mounted on the cross support lot a grinding machine. Secured tothis slide 2 is a plate 3 on which a slide 4 is vertically adjustablevia a threaded spindle 5 and the pairs of bevelgears 6 and 7 by means of the spindle 8 mounted in the cross support 1. The slide 4 has two lugs 9 in which the rest 10 is mounted by means of pointed screws 12. A swing bolt 13 enables the rest It) to be inclined at a certain angle in order to bring the cup wheel 14 into the desired position for grinding. Mounted so that it is rotatable and vertically adjustable in the rest 10 is a bush 15 in which the grind ing wheel spindle 17 is supported so that it is rotatable and axially immovable. The spindle 17 is driven via a belt pulley 18. The bush 15 has a thread 19 on which is arranged the worm gear 21 designed as a threaded nut. This gear 21 can be rotated by means of crank 24 through the worm 22 which is arranged on the shaft 23. The worm gear 21, pressed by the compression spring 26 bears against the fitting surface 25a of the collar 2:3 which is rigidly connected to the rest 10, whereby the axial mounting of the bush 15 is free from play. By rotating the worm gear 21, the bush 15'and thus the grinding wheel 14 can be vertically adjusted without the bush 15 turning.

Parallel to the bush 15, the bush 30 is mounted so that it is axially shiftable but not rotatable in the rollers 31 in the rest or support 10.. Mounted so that it is rotatable and axially shiftable in the bush 30 is the rod 32, secured to which is an arm 33 supporting the diamond dresser 34. The rod 32 has a neck 35 in which the roller 36 engages. The roller 36 is supported on a pivoted lever, not shown, which is swivellably mounted on the bolt 38 and locked in either of two positions. In one locked position the arm 33 can also be turned through 180 so that the diamond dresser 34 is over and dresses the top edge of the grinding wheel when it is intended to undergrind with the said wheel.

The bush 3% has a thread 30a on which is arranged the spur gear 45 designed as a threaded nut. By means of the spring 47, which pressesagainst the bush 3d, the spur gear $5 is forced against the rest 19 and thus the bush 3% is supported free from axial pl'ay. Via a worm gear 51 the feed-in motor drives the spindle 52 on which the spur gear 53 is arranged. The spur gear 53 engages both the spur gear 54; which is rigidly connected to the bush. 15, and the spur gear 45. Since the latter is arranged with female thread on the bush 36, it tightens or loosens the said bush. As the worm gear 21 and the worm 2.2 have a tooth system with self-locking pitch, the worm gear 21 actsas a stationary threaded nut in which the bush 15 is screwed downwards on. being rotated.

The female thread of the spur gear 45 and that of the worm gear 21 have exactly the' sarne pitch so that the rotation of the spur gear 53-causes the bushes l5 and to move upwards or downwards along an exactly similar path.

it is advisable to dress the grinding wheel by means of the diamond dresser 34 before each grinding. The grinding wheel is then brought into grinding contact with the workpiece 62 The grinding allowance 2 between the workpiece andthe template '61 can then be measured by means of the clock dial micrometer 63. To this end the. clock dial micrometer '63 is first applied to the worlo. piece in and then the machine table to which the workpiece and the template are secured is moved until the clock dial micrometer is positioned over the template 61, whereby the difference in level Z can be accurately read from the clock dial. The operator then transfers this reading by hand to the secondiclock dial micrometer 5'7, adjusting it by means of the set screw 56in such a manner that the switch 58a is operated somewhat before the set dimension is reached. With the feed motion of the grinding spindle or the bush3t), the pin 57a of the clock dial micrometer mountedonthe arm Btlb presses the arm of the switch 58 and. causes itito change. over. By this means, as will be explained in greater detail in the description of the wiring diagram, the circuit of the 7 motor 50 and thus the grinding wheel infeed is interrupted and a signal lamp lights. The operator now knows that there is only one more grinding stroke to come. Experience shows that, in order to obtain as smooth and fine a surface as possible, it is advantageous to dress the grinding. wheel once again before making the last grinding stroke. To this end the arm 33 with the diamond 34 is brought into the position indicated by the dash-dot line in Fig. 1 by operating the lever 76 (Fig. 3) and rotating the shaft 32. 'Since, While the grinding Wheel has been feeding towards the workpiece, the bush 30 has moved exactly the same axial distance as the bush 15, the diamond 34 would only barely touch the grinding wheel but not dress it. To permit the grinding wheel to be dressed, it must be lowered by means of the crank 24 which turns the worm gear 21 through the worm 22. While this is being done, the bush is locked by the wheel 54 through the shaft 52 and the worm gear 22 so that it cannot rotate. The worm gear 21 lies with its face against the ring 25, so that by turning the crank 24 an axial movement of the bush 15 results. To dress the grinding wheel 14 the crank 24 is now turned in such a direction that the grinding wheel moves towards the diamond 34 so that said wheel can be dressed. The surface of the grinding wheel coming into contact with the workpiece thus remains in exactly the same vertical position after dressing as before, so that the last grinding stroke can be made Without repeating the measurement.

There are thus two separate axial movements of the grinding wheel and it is important to distinguish between them. The automatic infeed of the grinding wheel towards the workpiece 62 is effected by the motor 50, the Worm gears 51, the shaft 52 and the spur gears 53, 54, the thread 19 turning in the stationary worm gear. The manual feed movement for dressing the grinding wheel is effected by rotating the worm gear 21 by means of the crank 24, there being no rotation of the bush 15. After the grinding wheel has been dressed, the grinding process is continued, whereby it is advantageous to change the feed by bringing into operation a so-called fine feed which may be obtained, for instance, by means of additional gears between the motor 50 and the shaft 52. On the preset nominal dimension being reached (final position) the switch 58b is automatically operated, thus cutting out the motor and lighting a signal lamp.

Electrical control of the device is effected as follows:

Operation of the switch 65 (Fig. 4) pulls up the relay 66, thus causing the capacitor of the time relay 69b to charge. In the extreme backward or forward position of the machine table the switch 74 or 75 respectively is switched over for a short time by a cam mounted on said machine table. In this way the relay 69 receives voltage from the capacitor 69b and cuts in the motor relay 68 through the contact 690, so that the feed-in motor 50 for the grinding wheel begins to turn. The discharge time of the capacitor and thus the time the motor continues to rotate, which determines the amount of the infeed, can be regulated by means of the potentiometer 70. Excessive feed motion is obviated by the motor relay 68 in its position of rest briefly closing the armature circuit through one of its contacts and thus braking the armature rotation. On the preliminary dimension fixed by means of the set screw 64 being reached, the automatic feed is interrupted through the contact 58a, whereupon the red signal lamp 59 lights. Further automatic infeed down to the final dimension can then take place only after the position of switch 73 has been changed.

Thus if the contact 58a is switched over by means of the screw 64, then the motor relay 68 and with it the feed-in motor 50 are immediately cut out and the signal lamp 59 is made to light.

6 After the position of switch 73 has been changed, the

capacitor 69b is charged again and the relay 68 can also receive voltage again by way of the relay 69 and its contact 69c. The automatic infeed continues until the switch 58b is also switched over. This interrupts all automatic infeed and the green signal lamp 60, which signifies final dimension reached, lights up.

For undergrinding, as for example in dovetail slideways etc., the device can be so designed that the grinding wheel infeed is effected in the opposite direction. The set screw 64 is then so set that in the course of the upward motion first the switch 58a is switched over and then the switch 58b. The selection of the feed direction, i. e. upward or downward motion, is made by means of switch 65.

Various changes and modifications may be made without departing from the spirit and scope of the present invention and it is intended that such obvious changes and modifications be embraced by the annexed claims.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent, is:

1. An apparatus for automatically feeding, in the direction of a workpiece, a grinding Wheel of a grinding machine having a rest, and a dresser for trueing said wheel; comprising a first bush arranged in said rest for axial displacement relative thereto and constituting bearing means for said grinding wheel, said bearing means supporting said wheel for rotation about its axis while restraining movement of said wheel lengthwise of its axis, whereby said grinding wheel may be fed in the direction of said workpiece upon axial displacement of said first bush in one direction, a second bush arranged in said rest for axial displacement relative to said rest and parallel to said first bush, said second bush constituting bearing means for said dresser and supporting the latter for rotary and axial movement relative to said second bush and substantially coaxially therewith, whereby said dresser maybe moved, respectively, toward and away from said grinding wheel upon axial and rotary movement with respect to said sec-0nd bush for trueing said wheel in a predetermined position thereof, drive means operatively connected to both said first bush and said second bush for axially displacing same jointly equal distances in the same direction, whereby both said wheel and said dresser are moved axially to the same extent, gauging means operatively connected to one of said bushes for indicating the extent of displacement of said one bush in the direction of said workpiece and thus the extent of feed of said grinding wheel in the direction of said workpiece during grinding operation, and control means operatively interconnected between said gauging means and said drive means for interrupting operation of the latter upon attainment of apredetermined extent of feed of said grinding wheel corresponding to a predetermined extent of grinding of said workpiece.

2. An apparatus according to claim 1, further comprising means supported by said rest for indicating the grinding allowance for said workpiece, and a set screw adjustably carried by said second bush, said gauging means including a dial micrometer having an actuating member engageable and displaceable by said set screw, whereby said micrometer may be set to a first reading equal to the reading of said indicating means through adjustment of said set screw, said control means comprising electric circuit means connected to said drive means and including switch means, said micrometer being provided with a pin responding to movement of said actuating member and operable to actuate said switch means, said pin being arranged to contact said switch means upon attainment of a predetermined reading on said micrometer, whereby upon displacement of said set screw with said second bush said switch means Will be actuated to interrupt operation of said drive means upon displacement of said grinding wheel a distance equal to the difference between said first reading and said predetermined reading of said micrometer.

3. An apparatus according to claim 1, said first bush being further arranged for rotary movement relative to said rest and being provided with an externally threaded portion, said second bush being provided with an externally threaded portion, first and second internally threaded nuts supported by said rest against movement lengthwise of their own axes and engaging, respectively, said threaded portions of said first bush and said second bush, said drive means being connected on the one hand to said first bush and on the other hand to said second nut and operable to rotate said first bush and said second nut jointly, to thereby displace both said first bush and said second bush axially of themselves within said rest.

4. An apparatus according to claim 3, said first threaded nut which is in engagement with said first bush being designed as a worm gear and being rotatably supported on said rest, a crank, a worm meshing with said worm gear and connected to said crank for rotation thereby, the teeth of said worm and said worm gear being constructed to have a self-locking pitch, whereby the grinding wheel can be vertically adjusted relative to said dresser without the height of the latter being altered.

5. An apparatus according to claim 3, further comprising a rigid stop on said rest and engaging said first nut, and a spring engaging said first bush in which said grinding wheel is supported and biasing said first nut against said stop, whereby axial play of said first bush and said grinding wheel is avoided.

6. An apparatus according to claim 3, further comprising a rigid stop on said rest and engaging said second nut, and a spring bearing on said second bush in which said dresser is supported and biasing said second nut against said stop, whereby axial play of said second bush and said dresser is avoided.

7. An apparatus according to claim 3, further comprising a template and a first clock dial micrometer positioned adjacent said rest for determining the grinding allowance for said workpiece.

8. An apparatus according to claim 7, further comprising a set screw adjustably carried by said second bush, and a second clock dial micrometer operatively connected to said set screw and settable by the latter, whereby the reading of said first dial micrometer may be transferred to said second dial micrometer, said control means including an electric circuit and a switch operable by said second micrometer.

9. An apparatus according to claim 8, said second clock dial micrometer and said switch being stationarily disposed on said rest.

10. An apparatus according to claim 3, further comprising means for locking said dresser at two difierent heights with respect to said second bush.

11. An apparatus according to claim 10, further comprising an arm supported by said second bush and extending substantially at right angles to the axis of the latter, said dresser being secured to said arm, whereby said dresser can be swung laterally of said grinding wheel toward and away from the latter, respectively.

12. An apparatus according to claim 11, said arm being 6 removably connected to said second bush, whereby said dresser may be disposed in an upwardly facing position and in a downwardly facing position, respectively, to contact said grinding wheel from below or from above.

13. An apparatus according to claim 1, further comprising first signal means connected to said control means and operable thereby to indicate a feed of said grinding wheel less than said predetermined extent of feed.

14. An apparatus according to claim 13, further comprising second signal means connected to said control means and operable to indicate completion of said predetermined extent of feed.

15. An apparatus according to claim 14, said first and second signal means comprising signal lamps, respectively, said control means including electric circuit means and switch means responsive to said gauging means for conditioning said electric circuit means, said lamps being connected to said electric circuit means.

16. In a grinding machine having a support, a cup grinding wheel, a shaft supporting said grinding wheel, a diamond dresser for trueing said Wheel, and a rod supporting said dresser; a first bush arranged in said support for axial displacement relative thereto toward and away from a workpiece to be ground, means rotatably mounting said shaft Within said first bush and coaxially therewith while restraining axial movement of said shaft relative to said first bush, whereby said grinding wheel may be fed in the direction of said workpiece upon axial displacement of said first bush in said direction, a second bush arranged in said support for axial displacement relative to said support and parallel to said first bush, means mounting said rod within said second bush and coaxially therewith for rotary and axial movement relative thereto, whereby said dresser may be moved, respectively, toward and away from said grinding wheel upon axial and rotary displacement of said rod with respect to said second bush for trueing said wheel in any position thereof, drive means operatively connected to both said first. bush and said second bush for axially displacing the same jointly and coextensively in the same direction, gauging means operatively connected to one of said bushes for indicating the extent of displacement of said one bush in the direction of said workpiece and thus the extent of feed of said grinding wheel in the direction of said workpiece during grinding operation, and control means operatively interconnected between said gauging means and said drive means for interrupting operation of the latter upon attainment of a predetermined extent of feed of said grinding wheel corresponding to a predetermined extent of grinding of. said workpiece.

References Cited in the file of this patent UNITED STATES PATENTS Philippe Sept. 5, 1939 

